get rid of gnome-keyring dependency on Linux OS

[mjhalwa]

To clarify: in the original post, I did already have python-dbus installed (as well as libsecret etc), I just did not have an actual backend for opensecrets installed (in my case gnome-keyring). The release linked in https://github.com/bohning/usdb_syncer/issues/136#issuecomment-1563521924 makes it error in a much nicer/more useful way.

Ideally it would actually start without gnome-keyring installed, it just disables certain login methods (I'm assuming the None method is the one which actually requires it, since the rest just reads some cookies)

Originally posted by @barbeque-squared in https://github.com/bohning/usdb_syncer/issues/136#issuecomment-1565422341